Stabilization systems from triarylphosphites and phenols

ABSTRACT

Stabilization system consisting of a triarylphosphite of the general formula ##STR1## wherein R 1  represents tert.-butyl, 1,1-dimethylpropyl, cyclohexyl or phenyl, and one of 
     R 2  and R 3  is hydrogen and the other is hydrogen, methyl, tert.-butyl, 1,1-dimethylpropyl, cyclohexyl or phenyl, 
     and a phenolic antioxidant, for stabilizing polyolefins.

This is a continuation of application Ser. No. 658,312 filed on Feb. 17,1976, now abandoned.

The present invention relates to the use of stabilisation systems fromtriarylphosphites and phenols for stabilising polyolefins againstthermooxidative deterioration, as well as to the polyolefins stabilisedtherewith.

The use of tri-esters of phosphorous acid as stabilisers in polyolefinsis known. Furthermore, in J. Voigt, "The Stabilisation of Plasticsagainst Light and Heat," 1st Edition, Springerverlag [Springerpublishing house] 1966, page 323, the combination of phosphorous acidesters with other antioxidants is put forward as being their preferredmode of application.

In particular, there is known from U.S. Pat. No. 3,558,554 the use ofthe three-component combination of "phosphite containing aryl groups" -"phenolic compounds" - "thiodialiphatic esters" in polyolefins.

Among the "phosphites containing aryl groups" there are many variablysubstituted (unsymmetrical) phosphites, i.e. those which undergointermolecular transesterification reactions, which are liquid and whichreadily hydrolyse, which results in poor storage stability and in aninadequate attainable effectiveness. Moreover, with the addition ofthiodialiphatic esters under the processing conditions, there isfrequently observed discolouration.

It is clear from GB No. 1,078,772 that the mixture of aryl-containingphosphites with o-substituted phenols in polyolefins exhibits aparticularly good stabilising effect. The high degree of effectivenessis attributed to the o-substituent in the phenol component.

In addition, there is described in U.S. Pat. No. 3,533,989 the specialtwo-component combination of 2,6-ditert.butyl-4-methylphenol withPolygard, (tris-p-nonyl-phenyl phosphites), as a stabiliser forpolyolefins. In the same patent specification there is shown the use oftris-(2-tert.butyl-4-methylphenyl)phosphite, optionally in combinationwith Polygard. Both combinations contain Polygard, which, as in the caseof the above mentioned phosphites, is an oily liquid having thedescribed disadvantages.

It has now been found that, surprisingly, a limited class of symmetricaltriarylphosphites of the general formula I ##STR2## wherein R₁represents tert.-butyl, 1,1-dimethylpropyl, cyclohexyl or phenyl, andone of R₂ and R₃ is hydrogen and the other is hydrogen, methyl,tert.-butyl, 1,1-dimethylpropyl, cyclohexyl or phenyl, display, incombination with phenolic antioxidants, a particular degree ofeffectiveness in polyolefins against degradation reactions andcross-linking reactions, such as those normally occurring in theprocessing of polyolefins.

This particular degree of effectiveness is reflected especially in theexcellent absence of discolouration in the resulting polymers, a resultwhich constitutes an advance compared with the results obtained in thecase of the prior-art three-component combination described in U.S. Pat.No. 3,558,554. Futhermore, the degree of effectiveness obtained isbetter than that obtained with the combinations with unsymmetricalphosphites as described in U.S. Pat. No. 3,558,554, or with thecombinations with tris-p-nonyl-phenyl phosphite as described in U.S.Pat. No. 3,533,989.

The compounds of the formula I can be used--together with one or more ofthe phenolic compounds--either singly or in combination with each other.The phosphites usable according to the invention are in most casescrystallised solids, which, compared with the wide range of phosphitesknown hitherto, are particularly stable also against hydrolysis.

The symbols in the formula I preferably have the following meanings:

R₁ represents tert.-butyl or 1,1-dimethylpropyl, and one of

R₂ and R₃ represents hydrogen, and the other represents hydrogen,methyl, tert.-butyl or 1,1-dimethylpropyl.

A particularly preferred embodiment is one wherein

R₁ represents tert.-butyl, and one of

R₂ and R₃ represents hydrogen, and the other represents hydrogen, methylor tert.-butyl.

Compounds of the formula I that are especially suitable are, forexample:

tris-(2,5-ditert.-butylphenyl)-phosphite,

tris-(2-tert.-butylphenyl)-phosphite,

tris-(2-phenylphenyl)-phosphite,

tris-[2-(1,1-dimethylpropyl)-phenyl]-phosphite,

tris-[2,4-di-(1,1-dimethylpropyl)-phenyl]-phosphite,

tris-(2-cyclohexylphenyl)-phosphite, and

tris-(2-tert.-butyl-4-phenylphenyl)-phosphite;

or, in particular:

tris-(2,4-ditert.-butylphenyl)-phosphite.

The following are be mentioned as examples of phenolic compounds:

1. Single 2,6-dialkylphenols, such as 2,6-di-tert.-butyl-4-methylphenol,2,6-di-tert.-butyl-4-methoxymethylphenol or2,6-di-tert.-butyl-4-methoxyphenol.

2. Bisphenols, such as2,2'-methylene-bis-(6-tert.-butyl-4-methylphenol),2,2'-methylene-bis-(6-tert.-butyl-4-ethylphenol),2,2'-methylene-bis-[4-methyl-6-(α-methylcyclohexyl)-phenol],1,1-bis-(5-tert.-butyl-4-hydroxy-2-methylphenyl)-butane,2,2-bis-(5-tert.-butyl-4-hydroxy-2-methylphenyl)-butane,2,2-bis-(3,5-di-tert.butyl-4-hydroxyphenyl)-propane,1,1,3-tris-(5-tert.butyl-4-hydroxy-2-methylphenyl)-butane,2,2-bis-(5-tert.-butyl-4-hydroxy-2-methylphenyl)-4-n-dodecylmercapto-butane,1,1,5,5-tetra-(5-tert.-butyl-4-hydroxy-2-methylphenyl)-pentane, ethyleneglycol-bis-[3,3-bis-(3'-tert.-butyl-4'-hydroxyphenyl)-butyrate],1,1-bis-(3,5-dimethyl-2-hydroxyphenyl)-3-(n-dodecylthio)-butane, or4,4'-thio-bis-(6-tert.-butyl-3-methylphenol).

3. Hydroxybenzyl aromates, such as1,3,5-tri-(3,5-di-tert.-butyl-4-hydroxybenzyl)-2,4,6-trimethylbenzene,2,2-bis-(3,5-di-tert.-butyl-4-hydroxybenzyl)-malonic acid-dioctadecylester, 1,3,5-tris-(3,5-di-tert.-butyl-4-hydroxybenzyl)-isocyanurate, or3,5-di-tert.-butyl-4-hydroxybenzyl-phosphonic acid-diethyl ester.

4. Amides of β-(3,5-di-tert.-butyl-4-hydroxyphenyl)-propionic acid, suchas1,3,5-tris-(3,5-di-tert.-butyl-4-hydroxyphenyl-propionyl)-hexahydro-s-triazine,N,N'-di-(3,5-di-tert.-butyl-4-hydroxyphenyl-propionyl)-hexamethylenediamine.

5. Esters of β-(3,5-di-tert.butyl-4-hydroxyphenyl)-propionic acid withmono- or polyvalent alcohols, such as with methanol, octadecanol,1,6-hexanediol, ethylene glycol, thiodiethylene glycol, neopentylglycol, pentaerythritol, tri-hydroxyethyl-isocyanurate.

6. Spiro compounds, such as diphenolic spiro-diacetals orspiro-diketals, such as 2,4,8,10-tetraoxaspiro-[5,5]-undecanesubstituted in the 3- and 9-position with phenolic radicals, such as3,9-bis-(3,5-di-tert.butyl-4-hydroxyphenyl)-2,4,8,10-tetraoxaspiro-[5,5]-undecane,3,9-bis-[1,1-dimethyl-2-(3,5-ditert.-butyl-4-hydroxyphenyl)-ethyl]-2,4,8,10-tetraoxaspiro-[5,5]-undecane.

Particularly preferred phenolic compounds are:

1,3,5-tri-(3,5-di-tert.-butyl-4-hydroxybenzyl)-2,4,6-trimethylbenzene,

pentaerythritol-tetra[3-(3,5-di-tert.-butyl-4-hydroxyphenyl)-propionate],

β-(3,5-di-tert.-butyl-4-hydroxyphenyl)-propionic acid-n-octadecyl ester,

thiodiethyleneglycol-β-[4-hydroxy-3,5-di-tert.-butyl-phenyl]-propionate,

2,6-di-tert.-butyl-4-methyl-phenol, and

3,9-bis-[1,1-dimethyl-2-(3,5-ditert.-butyl-4-hydroxyphenyl)-ethyl]-2,4,8,10-tetraoxaspiro-[5,5]-undecane.

The compounds of the formula I can be produced by methods known per se,for example by reaction of a phenol of the formula II ##STR3## withphosphorus trichloride, without solvent, at 20°-250° C., or in an inertaprotic solvent in the presence of an organic base, or by reaction of acompound of the formula II with triphenylphosphite, preferably withoutsolvent, in the presence of a basic catalyst.

The resulting compounds are purified by recrystallisation in a suitablesolvent (solvent mixture).

It is possible with the stabiliser mixture according to the invention tostabilise, for example, the following polyolefins:

1. polymers that are derived from singly unsaturated hydrocarbons, suchas polyolefins, e.g. polyethylene of low and high density, which canoptionally be cross-linked, polypropylene, polyisobutylene,polymethylbutene-1 and polymethylphentene-1;

2. mixtures of the homopolymers mentioned under 1., such as mixtures ofpolypropylene and polyethylene, polypropylene and polybutene-1,polypropylene and polyisobutylene;

3. copolymers of the monomers on which the homopolymers mentionedunder 1. are based, such as ethylene/propylene copolymers,propylene/butene-1 copolymers, propylene/isobutylene copolymers,ethylene/butene-1 copolymers, as well as terpolymers of ethylene andpropylene with a diene, such as hexadiene, di-cyclopentadiene orethylidenenorbornene.

The stabiliser mixture according to the invention is incorporated at aconcentration of 0.005% to 5%, preferably 0.01 to 1%, particularlypreferably 0.05 to 0.5%, calculated on the material to be stabilised.The triarylphosphite and the phenolic antioxidant are incorporated inthe ratio of 10:1 to 1:5, preferably 5:1 to 1:2, particularly 3:1 to1:1. Incorporation can be effected by various methods, for example bydry mixing of the polymer with at least one of the compounds of theinvention and a phenolic antioxidant, and subsequent processing in akneading machine, mixing rolls or extruder. The additives mentioned canbe applied also in the form of a solution or dispersion to the polymer,with the solvent being subsequently evaporated off.

The following may be mentioned as examples of further additives that canbe used together with the combination according to the invention:

1. Aminoaryl derivatives, e.g.

phenyl-1-naphthylamine, phenyl-2-naphthylamine,N,N'-diphenyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine,N,N'-di-2-naphthyl-p-phenylenediamine,N,N'-di-sec.-butyl-p-phenylenediamine,6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline,6-dodecyl-2,2,4-trimethyl-1,2-dihydroquinoline, mono- anddioctyliminodibenzyl, polymerised 2,2,4-trimethyl-1,2-dihydroquinoline.Octylated diphenylamine, nonylated diphenylamine,N-phenyl-N'-cyclohexyl-p-phenylenediamine,N-phenyl-N'-isopropyl-p-phenylenediamine,N,N'-di-sec.octyl-p-phenylenediamine,N-phenyl-N'-sec.-octyl-p-phenylenediamine,N,N'-di-(1,4-dimethylpentyl)-p-phenylenediamine,N,N'-dimethyl-N,N'-di-(sec.-octyl)-p-phenylenediamine,2,6-dimethyl-4-methoxyaniline, 4-ethoxy-N-sec.-butylaniline,diphenylamineacetone condensation product, aldol-1-naphthylamine andphenothiazine.

With the use of this group, discolouration effects have to be taken intoaccount.

2. UV-Absorbers and light-stabilising agents

2.1. 2-(2'-Hydroxyphenyl)-benzotriazoles, e.g. the 5'-methyl-,3',5'-di-tert.-butyl-, 5'-tert.-butyl-, 5'-(1,1,3,3-tetramethylbutyl)-,5-chloro-3',5'-di-tert.-butyl-, 5-chloro-3'-tert.-butyl-5'-methyl-,3'-sec.-butyl-5'-tert.-butyl-, 3'-α-methylbenzyl-5'-methyl-,3'-α-methylbenzyl-5'-methyl-5-chloro-, 4'-hydroxy-, 4'-methoxy-,4'-octoxy-, 3',5'-di-tert.-amyl-, 3'-methyl-5'-carbomethoxyethyl- and5-chloro-3',5'-di-tert.-amyl-derivative.

2.2. 2,4-bis-(2'-Hydroxyphenyl)-6-alkyl-s-triazines, e.g. the 6-ethyl-,6-heptadecyl- or 6-undecyl-derivative.

2.3. 2-Hydroxybenzophenones, e.g. the 4-hydroxy-, 4-methoxy-, 4-octoxy-,4-decyloxy-, 4-dodecyloxy-, 4-benzyloxy-, 4,2',4'-trihydroxy- or2'-hydroxy-4,4'-dimethoxy-derivative.

2.4. 1,3-bis-(2'-Hydroxybenzoyl)-benzenes, e.g.1,3-bis-(2'-hydroxy-4'-hexyloxy-benzoyl)-benzene,1,3-bis-(2'-hydroxy-4'-octyloxy-benzoyl)-benzene or1,3-bis-(2'-hydroxy-4'-dodecyloxy-benzoyl)-benzene.

2.5. Esters of optionally substituted benzoic acids, e.g.phenylsalicylate, octylphenylsalicylate, dibenzoylresorcin,bis-(4-tert.-butylbenzoyl)-resorcin, benzoylresorcin,3,5-di-tert.-butyl-4-hydroxybenzoic acid-2,4-di-tert.-butylphenyl esteror -octadecyl ester or -2-methyl-4,6-di-tert.-butyl ester.

2.6. Acrylates, e.g. α-cyano-β,β-diphenylacrylic acid-ethyl ester or-isooctyl ester, α-carbomethoxy-cinnamic acid methyl ester,α-cyano-β-methyl-p-methoxy-cinnamic acid methyl ester or -butyl ester orN-(β-carbomethoxyvinyl)-2-methyl-indoline.

2.7. Nickel compounds, e.g. nickel complexes of2,2'-thio-bis-[4-(1,1,3,3-tetramethylbutyl)-phenol], such as the 1:1- or1:2-complex, optionally with additional ligands such as n-butylamine,triethanolamine or N-cyclohexyl-di-ethanolamine, nickel complexes ofbis-[2-hydroxy-4-(1,1,3,3-tetramethylbutyl)-phenyl]-sulphone, such asthe 2:1-complex, optionally with additional ligands such as2-ethylcapronic acid, nickel-dibutyldithiocarbamate, nickel salts of4-hydroxy-3,5-di-tert.-butylbenzyl-phosphonic acid-monoalkyl esters,such as of methyl, ethyl or butyl esters, nickel complexes of ketoximes,such as of 2-hydroxy-4-methyl-phenyl-undecylketonoxime,nickel-3,5-di-tert.-butyl-4-hydroxybenzoate ornickel-isopropylxanthogenate.

2.8 Sterically hindered amines, e.g.4-benzoyl-2,2,6,6-tetramethylpiperidine,4-stearoyloxy-2,2,6,6-tetramethylpiperidine,bis-(2,2,6,6-tetramethylpiperidyl)-sebacate or3-n-octyl-7,7,9,9-tetramethyl-1,3,8-triaza-spiro[4,5]decane-2,4-dione.

2.9. Oxalic acid diamides, e.g. 4,4'-di-octyloxy-oxanilide,2,2'-di-octyloxy-5,5'-di-tert.-butyl-oxanilide,2,2'-di-dodecyloxy-5,5'-di-tert.-butyl-oxanilide,2-ethoxy-2'-ethyl-oxanilide, N,N'-bis-(3-dimethylaminopropyl)-oxalamide,2-ethoxy-5-tert.-butyl-2'-ethyloxanilide and the mixture thereof with2-ethoxy-2'-ethyl-5,4'-di-tert.-butyl-oxanilide, or mixtures of ortho-and para-methoxy- as well as of o- and p-ethoxy-disubstitutedoxanilides.

3. Metal deactivators, e.g.

oxanilide, isophthalic acid dihydrazide, sebacicacid-bis-phenylhydrazide, bis-benzylidene-oxalic acid dihydrazide,N,N'-diacetal-adipic acid dihydrazide, N,N'-bis-salicyloyloxalic aciddihydrazide, N,N'-bis-salicyloylhydrazine,N,N'-bis-(3,5-di-tert.-butyl-4-hydroxyphenylpropionyl)-hydrazine,N-salicyloyl-N'-salicylalhydrazine, 3-salicyloylamino-1,2,4-triazole orN,N'-bis-salicyloyl-thiopropionic acid dihydrazide.

4. Basic co-stabilisers, e.g.

alkali metal salts and alkaline-earth metal salts of higher fatty acids,for example Ca-stearate, Zn-stearate, Mg-behenate, Na-ricinoleate orK-palmitate.

5. Nucleation agents, e.g.

4-tert.-butylbenzoic acid, adipic acid or diphenylacetic acid.

6. Other additives, e.g.

lubricants, e.g. particularly preferred: stearyl alcohol, fillers,carbon black, asbestos, kaolin, talcum, glass fibres, pigments, opticalbrighteners, flameproofing agents and antistatic agents.

The invention is further illustrated in the following Examples.Percentages (%) denote therein percent by weight, calculated on thematerial to be stabilised.

EXAMPLE I

100 Parts of unstabilised polyethylene of high density having amolecular weight of about 500,000 ("Lupolen 5260 Z" in powder form fromBASF) are in each case mixed dry with 0.05 part ofpentaerythritol-tetra-[3-(3,5-di-tert.-butyl-4-hydroxyphenyl)-propionate]and 0.1 part of a stabiliser of the following Table 1 or 2. The mixturesare kneaded in a Brabender plastograph at 220° C. and at 50 r.p.m. for20 minutes. During this time, the resistance to kneading is continuouslyrecorded as a torsional moment. Owing to cross-linking of the polymer,there occurs during the kneading period, after an initial constantstage, a rapid increase of the torsional moment. The effectiveness ofthe stabilisers is reflected in a lengthening of the time of constanttorsional moment.

The mixtures are subsequently removed from the plastograph and pressedout in a platen press at 260° platen temperature to sheets 1 mm thick,the appearance of which is visually assessed with respect to colour. Forthe assessment of discolouration in Tables 1 and 2, there is used anempirical colour scale wherein 5 denotes colourlessness, 4 a justperceptible discolouration, and 3, 2, 1 and <1 denote a successivelymore severe discolouration.

                  Table 1                                                         ______________________________________                                        Effectiveness of the stabiliser combinations of the invention                              Time in minutes                                                                             Discolouration                                                  until change of                                                                             assessment of the                                  Phosphite stabiliser                                                                       torsional moment                                                                            sheet specimens                                    ______________________________________                                        none         31/2          5                                                  tris-(2,4-di-tert.-butyl-                                                     phenyl)-phosphite                                                                          10            4-5                                                tris-(2-tert.-butyl-4-                                                        methylphenyl)-phosphite                                                                     101/2        4                                                  tris-(2-tert.-butyl-5-                                                        methylphenyl)-phosphite                                                                     9            4                                                  ______________________________________                                    

                  Table 2                                                         ______________________________________                                        Effectiveness of the unsymmetrical triphosphites described                    in US 3,558,554                                                                            Time in minutes                                                                             Discolouration                                                  until change of                                                                             assessment of the                                  Phosphite stabiliser                                                                       torsional moment                                                                            sheet specimens                                    ______________________________________                                        none         31/2          5                                                  di-n-butyl-(2-tert.-                                                          butyl-4-methylphenyl)-                                                        phosphite    4             4                                                  di-phenyl-(2-tert.-                                                           butyl-4-methylphenyl)-                                                        phosphite    41/2          4-5                                                di-n-butyl-(2,6-di-tert.-                                                     butyl-4-methylphenyl)-                                                        phosphite    61/2          2 (speckled                                                                   inhomogeneous)                                     ______________________________________                                    

From the results shown in Tables 1 and 2 it is clear that, compared withthe comparative products given in Table 2, the triarylphosphites of theformula I in Table I display in polyolefins a very high degree ofeffectiveness. In particular the concomitant use ofdilaurylthiodipropionate leads to a plastics material having poor colourproperties.

EXAMPLE II

100 Parts of unstabilised polyethylene of high density having amolecular weight of about 500,000 ("Lupolen 5260 Z" in powder form fromBASF) are in each case mixed dry with 0.1 part ofdilaurylthiodipropionate and with the stabilisers shown in the followingTable 3. The mixtures are kneaded in a Brabender plastograph at 220° C.and 50 r.p.m. for 20 minutes. During this time, the resistance tokneading is continuously recorded as a torsional moment. As aconsequence of cross-linking of the polymer there occurs in the courseof kneading, after an initial constant condition, a rapid rise of thetorsional moment. The effectiveness of the stabilisers is expressed in alengthening of the time of constant torsional moment. The mixtures aresubsequently removed from the plastograph and pressed out in a platenpress at 260° C. platen temperature into the form of 1 mm thick sheets,the appearance of which is visually assessed with respect to colour. Forthe assessment of discolouration in Table 3, there is used an empiricalcolour scale wherein 5 denotes colourlessness, 4 denotes a slightdiscolouration just perceptible, and 3, 2, 1 and <1 denote asuccessively more severe discolouration.

                  Table 3                                                         ______________________________________                                                        Time in minutes                                                                           Discolouration                                                    unitl change of                                                                           assessment of                                                     torsional   the sheet                                         Parts of stabiliser                                                                           moment      specimens                                         ______________________________________                                        0.05 part of pentaerythritol-                                                 tetra-3-(3,5-di-tert.-butyl-                                                                   21/2        1                                                4-hydroxyphenyl)-propionate                                                   0.05 part of pentaerythritol-                                                 terta-3-(3,5-di-tert.-butyl-                                                  4-hydroxyphenyl)-propionate                                                   + 0.1 part of tris-(2-tert.-                                                  butyl-4-methylphenyl)-                                                                        5           <1                                                phosphite                                                                     0.05 part of pentaerythritol-                                                 tetra-3-(3,5-ditert.-butyl-                                                   4-hydroxyphenyl)-propionate                                                   + 0.1 part of tris-(2,4-                                                      ditert.-butylphenyl)-                                                                         6           <1                                                phosphite                                                                     0.05 part of 1,1,3-tris-                                                      (5-tert.-butyl-4-hydroxy-                                                                      51/2       <1                                                2-methylphenyl)-butane                                                        0.05 part of 1,1,3-tris-                                                      (5-tert.-butyl-4-hydroxy-                                                     2-methylphenyl)-butane                                                        + 0.1 part of tris-(2-tert.-                                                  butyl-4-methylphenyl)-                                                                        9           <1                                                phosphite                                                                     0.05 part of 2,6-di-tert.-                                                    butyl-4-methylphenol                                                                          5           <1                                                0.05 part of 2,6-di-tert.-                                                    butyl-4-methylphenol                                                          + 0.1 part of tris-(2-                                                        tert.-butyl-4-methyl-                                                                         101/2       <1                                                phenyl)-phosphite                                                             ______________________________________                                    

The results show that, independent of the employed antioxidant, there isobtained with the concomitant use of dilaurylthiodipropionate a plasticsmaterial which has poor colour properties and which gives in some caseslow times of constant torsional moment.

EXAMPLE III

100 Parts of unstabilised polyethylene of high density having amolecular weight of about 500,000 ("Lupolen 5260 Z" in powder form fromBASF) are mixed dry with the stabilisers of the following Table 4 in thegiven concentrations. The mixtures are kneaded in a Brabenderplastograph at 220° C. and 50 r.p.m. for 20 minutes. During this timethe resistance to kneading is continuously recorded. As a consequence ofcross-linking of the polymer, there occurs in the course of the kneadingprocess, after an initial constant condition, a rapid rise in thetorsional moment. The effectiveness of the stabilisers is expressed in alengthening of the time of constant torsional moment.

                  Table 4                                                         ______________________________________                                                               Time in minutes                                                               to change of the                                       Parts of stabiliser    torsional moment                                       ______________________________________                                        none                   2                                                      0.15 part of pentaerythritol-tetra-                                           [3-(3,5-di-tert.-butyl-4-hydroxy-                                             phenyl)-propionate]    6                                                      0.15 part of tris-(2-tert.-butyl-                                             4-methylphenyl)-phosphite                                                                            4                                                      0.05 part of pentaerythritol-tetra-                                           [3-(3,5-di-tert.-butyl-4-hydroxy-                                             phenyl)-propionate]    101/2                                                  + 1.10 part of tris-2-tert.-butyl-                                            4-methylphenyl)-phosphite                                                     ______________________________________                                    

It follows from the data that with the same total concentration thecombination according to the invention produces a protective effect thatis clearly better compared with that obtained with the stabilisers usedseparately.

EXAMPLE IV

100 Parts of unstabilised polyethylene of high density having amolecular weight of about 500,000 ("Lupolen 5260 Z" in powder form fromBASF) are in each case mixed dry with 0.1 part oftris-(2-tert.-butyl-4-methylphenyl)-phosphite and 0.05 part of thephenolic antioxidants shown in the following Table 5. The mixtures arekneaded in a Brabender plastograph at 220° and 50 r.p.m. for 20 minutes.During this time, the resistance to kneading is continuously recorded asa torsional moment. As a consequence of cross-linking of the polymerthere occurs in the course of kneading, after an initial constant phase,a rapid rise of the torsional moment. The effectiveness of thestabilisers is expressed in a lengthening of the time of constanttorsional moment

                  Table 5                                                         ______________________________________                                                               Time in minutes                                                               to change of the                                       Phenolic antioxidant   torsional moment                                       ______________________________________                                        none                   4                                                      pentaerythritol-tetra-[3-(3,5-di-                                             tert.-butyl-4-hydroxyphenyl)-                                                 propionate             101/2                                                  1,1,3-tris-(5-tert.-butyl-4-                                                  hydroxy-2-methylphenyl)-butane                                                                       8                                                      3-(3,5-di-tert.-butyl-4-hydroxy-                                              phenyl)-propionic acid-octadecyl-                                             ester                  7                                                      1,3,5-tri-(3,5-di-tert.-butyl-4-                                              hydroxybenzyl)-2,4,6-trimethyl-                                               benzene                8                                                      2,2'-methylene-bis-(6-tert.-butyl-                                            4-methylphenol)        10                                                     4,4'-thiobis-(6-tert.-butyl-3-                                                methylphenol)          11                                                     ______________________________________                                    

The results show that with a wide selection of phenolic compounds incombination with the triarylphosphites according to the invention thereis obtained an excellent stabilisation of polyethylene of high density.

EXAMPLE V

100 Parts of unstabilised polyethylene of high density having amolecular weight of about 500,000 ("Lupolen 5260 Z" in powder form fromBASF) are mixed dry with the stabilisers given in Table 6 at the givenconcentrations. The mixtures are kneaded in a Brabender plastograph at220° C. and 50 r.p.m. for 20 minutes. The resistance to kneading duringthis time is continuously recorded as a torsional moment. As aconsequence of cross-linking of the polymer there occurs in the courseof kneading, after an initial constant condition, a rapid increase ofthe torsional moment. The effectiveness of the stabilisers is expressedin a lengthening of the time of constant torsional moment.

                  Table 6                                                         ______________________________________                                        Effectiveness of the stabiliser combinations according                        to the invention compared with that of the systems                            described in US 3,533,989.                                                                     Time in minutes unitl change                                 Parts of stabiliser                                                                            of the torsional moment                                      ______________________________________                                        0.05 parts of 2,6-ditert.-                                                    butyl-4-methylphenol                                                          + 0.1 part of tris-(2-tert.-                                                  butyl-4-methylphenyl)-                                                        phosphite        10                                                           0.05 part of 2,6-ditert.-                                                     butyl-4-methylphenol                                                          + 0.1 part of tris-(2,4-                                                      ditert.-butylphenyl)-                                                         phosphite        12                                                           0.05 part of 2,6-ditert.-                                                     butyl-4-methylphenol                                                          + 0.1 part of Polygard                                                        (tris-p-nonylphenyl-                                                          phosphite         5                                                           0.15 part of tris-(2-tert.-                                                   butyl-4-methylphenyl)-                                                        phosphite         4                                                           ______________________________________                                    

EXAMPLE VI

100 Parts of unstabilised polyethylene of high density having amolecular weight of about 500,000 ("Lupolen 5260 Z" in powder form fromBASF) are mixed dry with 0.05 part of3-(3,5-di-tert.-butyl-4-hydroxyphenyl)-propionic acid-octadecyl esterand 0.1 part of tris-(2-tert.-butyl-4-methylphenyl)-phosphite.

250 kg of this mixture is processed in an extrusion-blow apparatus (TypeVB 250, VOITH) at 227° C. nozzle temperature into the form of 120-literbarrels (frequency: 10 minutes per shot; 1 shot: 10 kg of material). Thebarrels have a smooth inner surface and are free of lattice orhoney-comb structure. Lattice or honey-comb structure or a rough innersurface are the result of an occurring cross-linking of the material.

EXAMPLE VII

100 Parts of polypropylene powder (Propathen HF 20, ICI) arehomogeneously mixed with the stabilisers listed in the following Table 7at the stated concentrations. The mixtures obtained are extruded andgranulated five times in succession in a single screw extruder at amaximum of 260° C. (temperature of the discharge zone) and 100 r.p.m.

The melt index of the material is measured after the 1st, 3rd and 5thextrusion. The load is 2160 g at 230° C.; the melt index is given ing/10 min. The degradation of the material is indicated by an increase ofthe melt index.

                  Table 7                                                         ______________________________________                                                              Melt index                                                                    after given num-                                                              ber of extrusions                                       Parts of stabiliser     1      3      5                                       ______________________________________                                        none                        14     42   76                                    0.15 part of pentaerythritol-tetra-                                           [3-(3,5-di-tert.-butyl-4-hydroxy-                                             phenyl)-propionate]         4.8    6.5  9.0                                   0.15 part of tris-(2,4-di-tert.-                                              butylphenyl)-phosphite      4.0    8.0  12.3                                   0.075 part of pentaerythritol-tetra-                                         [3-(3,5-di-tert.-butyl-4-hydroxy-                                             phenyl)-propionate]                                                                                       3.5    5.0  7.4                                   +0.075 part of tris-(2,4-di-tert.-                                            butylphenyl)-phosphite                                                        0.05 part of pentaerythritol-tetra-                                           [3-(3,5-di-tert.-butyl-4-hydroxy-                                             phenyl)-propionate]                                                                                       3.3    4.9  6.6                                   +0.1 part of tris-(2,4-di-tert.-                                              butylphenyl)-phosphite                                                        0.03 part of pentaerythritol-tetra-                                           [3-(3,5-di-tert.-butyl-4-hydroxy-                                             phenyl)-propionate                                                                                        3.2    4.5  6.5                                   +0.12 part of tris-(2,4-di-tert.-                                             butylphenyl)-phosphite                                                        0.15 part of 3,9-bis-[1,1-di-                                                 methyl-2(3,5-di-tert.-butyl-4-                                                hydroxyphenyl)-ethyl]2,4,8,10-                                                tetraoxaspiro-[5,5]undecane 4.9    6.8  9.0                                   0.05 part of 3,9-bis-[1,1-di-                                                 methyl-2(3,5-di-tert.-butyl-4-                                                hydroxyphenyl)-ethyl]2,4,8,10-                                                tetraoxaspiro-[5,5]undecane                                                                               3.4    4.5  6.2                                   +0.1 part of tris-(2,4-di-tert.-                                              butylphenyl)-phosphite                                                        ______________________________________                                    

We claim:
 1. A stabilized composition consisting essentially of(a) a polymer that is derived from a singly unsaturated acyclic hydrocarbon, or mixtures or copolymers thereof and (b) from 0.005 to 5% of a mixture of (1) a triarylphosphite of the general formula ##STR4## wherein R₁ represents tert-butyl, or 1,1-dimethylpropyl,R₂ represents methyl, tert-butyl, or 1,1-dimethylpropyl, and (2) a hindered phenolic antioxidant selected from the group consisting of 1,3,5-tris-(3',5'-di-t.butyl-4-hydroxybenzyl)-isocyanurate, 1,3,5-tris-(3,5-di-t.butyl-4-hydroxybenzyl)-2,4,6-trimethylbenzene, ethyleneglycol-bis(3,3-bis-3'-t.butyl-4'-hydroxyphenyl)-butyrate, pentaerylthrit-tetra-[3-(3,5-di-t.butyl-4-hydroxyphenyl)-propionate], thiobisethyleneglycol-bis-[3-(3,5-di-t.butyl-4-hydroxyphenyl)-propionate], hexamethylene-1,6-di-[3-(3,5-di-t.butyl-4-hydroxyphenyl)-propionate] and β-(3,5-di-t.butyl-4-hydroxyphenyl)-propionic acid-n-octadecyl ester, the ratio of the phosphite to the antioxidant being from 10:1 to 1:5.
 2. A stabilized composition of claim 1 wherein the hindered phenolic antioxidant is pentaerithritol tetrakis 3-(3,5-di-tert.-butyl-4-hydroxyphenyl) propionate.
 3. A composition of claim 2 wherein the triarylphosphite is tris-(2,4-di-tert-butylphenyl)phosphite.
 4. A composition of claim 2 wherein the triarylphosphite is tris-(2-tert-butyl-4-methylphenyl)-phosphite.
 5. A composition of claim 2 wherein the polymer is polyethylene or polypropylene.
 6. A composition of claim 4 wherein the polymer is polyethylene or polypropylene.
 7. A composition claim of 1, wherein the triarylphosphite is tris-(2,4-di-tert-butylphenyl)phosphite.
 8. A composition of claim 1, wherein the triarylphosphite is tris-(2-tert-butyl-4-methyl)-phosphite.
 9. A composition of claim 1, wherein the polymer is polyethylene or polypropylene.
 10. A composition of claim 8, wherein the polymer is polyethylene or polypropylene.
 11. A method of stabilizing polymers derived from singly unsaturated, acyclic hydrocarbons or mixtures or copolymers thereof during processing which comprises incorporating in said polymer 0.005 to 5% of a mixture consisting essentially of(a) a triarylphosphite of the general formula ##STR5## wherein R₁ represents tert-butyl, or 1,1-dimethylpropyl;R₂ represents methyl, tert-butyl, or 1,1-dimethylpropyl, and (b) hindered phenolic antioxidant selected from the group consisting of 1,3,5-tris-(3',5'-di-t.butyl-4-hydroxybenzyl)-isocyanurate, 1,3,5-tris-(3,5-di-t.butyl-4-hydroxybenzyl)-2,4,6-trimethylbenzene, ethyleneglycol-bis(3,3-bis-3'-t.butyl-4'-hydroxyphenyl)-butyrate, pentaerylthrit-tetra-[3-(3,5-di-t.butyl-4-hydroxyphenyl)-propionate], thiobisethyleneglycol-bis-[3-(3,5-di-t.butyl-4-hydroxyphenyl)-propionate], hexamethylene-1,6-di-[3-(3,5-di-t.butyl-4-hydroxyphenyl)-propionate] and β-(3,5-di-t.butyl-4-hydroxyphenyl)-propionic acid-n-octadecyl ester, wherein the phosphite to the antioxidant ratio is 10:1 to 1:5.
 12. A method of claim 11 wherein the hindered phenolic antioxidant is pentaerithritol tetrakis 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate.
 13. A method of stabilizing according to claim 12, wherein the triarylphosphite is tris-(2,4-di-tert.-butylphenyl)-phosphite.
 14. A method of stabilizing according to claim 12, wherein the triaryphosphite is tris-(2-tert.-butyl-4-methylphenyl)-phosphite.
 15. A method according to claim 12, wherein the polymer is propylene or polyethylene.
 16. A method according to claim 13, characterized in that the polymer is polyethylene or polypropylene.
 17. A method of stabilizing according to claim 11, wherein the triarylphosphite is tris-(2,4-di-tert-butyl-phenyl)phosphite.
 18. A method of stabilizing according to claim 11, wherein thr triarylphosphite is tris-(2-tert-butyl-4-methylphenyl)-phosphite.
 19. A method according to claim 11, wherein the polymer is propylene or polyethylene.
 20. A method according to claim 16, characterized in that the polymer is polyethylene or polypropylene. 